The invention relates to the use of dialkylmalamides to reduce the surface tension in water-based systems.
The ability to reduce the surface tension of water is of great importance in waterborne coatings, inks, adhesives, fountain solutions and agricultural formulations because decreased surface tension translates to enhanced substrate wetting in actual formulations. Surface tension reduction in water-based systems is generally achieved through the addition of surfactants. Performance attributes resulting from the addition of surfactants include enhanced surface coverage, fewer defects, and more uniform distribution. Equilibrium surface tension performance is important measure of the ability of a surfactant to reduce surface tension in aqueous systems when the system is at rest.
Traditional nonionic surfactants, such as alkylphenol or alcohol ethoxylates and ethylene oxide (EO)/propylene oxide (PO) copolymers, and anionic surfactants, such as sodium dialkyl sulfosuccinates, have good equilibrium surface tension performance. However, many of these surfactants are foamy and this can lead to problems in applications such as coatings, inks, adhesives, fountain solutions, agricultural formulations, electronic chemicals and cleaning formulations, and other applications where foam can lead to surface defects, poor adhesion, and processing difficulties. Additionally, anionic surfactants can impart water sensitivity to the finished coating.
In addition to the development of high-performance surfactants, there is considerable interest in the industry in surfactants with improved environmental characteristics. Environmental concerns have led to an increased use of environmentally compatible surfactants as alternatives have become available. In addition, the use of less favorable products, such as alkylphenol ethoxylate (APE) surfactants, has declined. This is, in part, due to the poor environmental characteristics of APE surfactants, such as incomplete biodegradation and a suspicion that they may function as endocrine mimics. The demand for high-performance, eco-friendly surfactants has stimulated efforts in new surfactant development. From this work a new family of surfactants, referred to as alkyl polyglycoside (APG) surfactants, has emerged as a readily biodegradable, environmentally-friendly alternative to conventional surfactants. These materials can be foamy and thus are not suitable for many coating, ink, adhesive, fountain solution, agricultural, and electronic chemical and cleaning applications where the generation of foam is undesirable.
Thus, not only is it desirable to obtain surfactants which exhibit excellent surface tension reducing capabilities and low foam, but it is also highly desirable that such new surfactants are environmentally-friendly. Moreover, since there is substantial interest in the development of environmentally-friendly surfactants, an essential attribute would be that these new surfactants not only possess the aforementioned desired performance properties but also are derived from naturally occurring compounds or their synthetic equivalents.
The importance of reducing surface tension in applications such as coatings, inks, adhesives, agricultural formulations, and electronic chemical and cleaning is well-appreciated in the art. The ability to lower the surface tension of aqueous media without producing foam is critical when one wants to wet low energy or contaminated substrates. In J. C. Padget""s article entitled xe2x80x9cAdditives for Water-based Coatingsxe2x80x94A Polymer Chemist""s Viewxe2x80x9d in Additives for Water-based Coatings, D. R. Karsa, ed., Cambridge, UK: Royal Society of Chemistry, 1990, pp. 1-29, the importance of surfactants in lowering the surface tension of aqueous systems in order to achieve wetting on low energy materials such as plastics and oily steel is highlighted.
In the graphic arts, it is well-known that surfactants lower the surface tension of aqueous media and thus aid in printing on lower energy substrates such as plastics, coated papers, coated cardboards, and foils and in wetting pigments to produce dispersions. In Dispersions: Characterization, Testing, and Measurement, Marcel Dekker, Inc., 1990, there is an entire chapter devoted to the topic of wettability and the necessity of lowering surface tension in order to achieve displacement of air from around small pigment particles and allow wetting and spreading on the pigment surface. Surfactants are known to act as wetting agents to moisten hydrophobic areas of the printing plate in offset printing (R. Kubler, xe2x80x9cPrinting Inks,xe2x80x9d in Ullmann""s Encyclopedia of Industrial Chemistry, Vol. A22, 1993, pp. 143-156), and certain surfactants have been beneficial in reducing foam generation in the ink fountain in flexographic and rotogravure printing inks (R. W. Bassemir, et al., xe2x80x9cInks,xe2x80x9d in Kirk-Othmer Encyclopedia of Chemical Technology, 4th Edition, Vol. 14, pp. 482-503).
In addition, the demands of the semiconductor fabrication industry have led to the requirement for high performance surfactants and wetting agents for photoresist developer formulations. As line features shrink to smaller sizes and photoresist substrate materials become more aliphatic in nature (i. e., lower surface energy), aqueous developer solutions increasingly are being formulated with surface tension reducing agents. An additional requirement for these developers, accentuated by the move toward larger wafer sizes, is that they exhibit low foam. This is particularly important when the so-called spray puddle techniques are used in applying the developer solution, wherein the developer is sprayed over increasingly larger areas. Even in cases where puddle or immersion techniques are used, microbubble entrainment during spreading of the solution over the photoresist surface can lead to defects. Other applications in the electronics industry using aqueous processing media would also benefit from good wetting and low foam.
Tetramethylammonium hydroxide (TMAH) is the chemical of choice in aqueous alkaline solutions for developing photoresists according to Microlithography, Science and Technology, J. R. Sheats and B. W. Smith, editors, Marcel Dekker, Inc., 1998, pp. 551-553. Surfactants are added to the aqueous TMAH solutions to reduce development time and scumming and to improve surface wetting.
A few examples of amides of malic acid (2-hydroxybutanedioic acid), also called malamides, are known. L-Malic acid occurs naturally as the predominant acid in many fruits, including apples, persimmons, quince and watermelons. It is classified as GRAS (Generally Recognized As Safe) by the U.S. Food and Drug Administration and is commonly used as a food acidulant. L-Malic acid is produced commercially from aqueous fumaric acid using immobilized Brevibacterium flavum cells in carrageenan. The racemic form, DL-malic acid, is also known. It is produced by hydration of maleic acid at elevated temperature and pressure.
In the literature, malic acid amides have been reported. However, the ability of malamides to lower surface tension in aqueous media has never been studied or realized.
Dermer and George, Proceedings of the Oklahoma Academy of Science, 1972, 52, pp. 66-69, describe the preparation of several malamides via reaction of the malate esters with primary amines. Malamides based on ethyl, isopropyl, cyclohexyl, hydroxyethyl and benzyl amines were isolated and characterized.
DE 4424533 A1 broadly discloses oligohydroxy dicarboxylic acid derivatives, including certain malamides derived from fatty alkyl amines, as synthetic barrier lipids in skin care products.
U.S. Pat. No. 5,359,129, discloses many malic acid derivatives, specifically including the acetate of lauryl malamide, and methods for treatment of psoriasis using such compositions.
U.S. Pat. No. 5,776,494 discloses the use of alkyl amides of di- and tri-carboxylic acids as gelling agents in non-aqueous pharmaceutical compositions.
This invention provides water-based compositions containing an organic or inorganic compound, particularly aqueous organic coating, ink, adhesive, fountain solution, agricultural and electronics cleaning compositions, having reduced surface tension by incorporation of an effective amount of an N,Nxe2x80x2-dialkylamide of malic acid, herein referred to as a malamide, of the following structure: 
where R1 and R2 are C4 to C10 alkyl groups, and preferably at least one of R1 and R 2 is a branched C4 to C10 alkyl group. It is also desirable that an aqueous solution of the malamide demonstrate an equilibrium surface tension of less than 52 dynes/cm at a concentration of no more than 5 wt % in water at 25xc2x0 C. using the Wilhelmy plate method. The Wilhelmy plate method of measuring surface tension is described in L. Wilhelmy""s article in Ann. Phys. 1863, 119, 177, which is incorporated by reference.
By xe2x80x9cwater-basedxe2x80x9d, xe2x80x9caqueousxe2x80x9d or xe2x80x9caqueous mediumxe2x80x9d, we mean, for purposes of this invention, a solvent or liquid dispersing medium which comprises at least 90 wt %, preferably at least 95 wt %, water. Obviously, an all water medium is also included.
Also provided is a method for lowering the equilibrium surface tension of such aqueous compositions by the incorporation of these malamide compounds.
Also provided is a method for applying a coating of a water-based inorganic or organic compound-containing composition to a surface to partially or fully coat the surface with the water-based composition, the composition containing an effective amount of a malamide compound of the above structure for reducing the equilibrium surface tension of the water-based composition.
There are significant advantages associated with the use of these malamides in water-based, organic-compound containing compositions, such as water-based coatings, inks, adhesives, fountain solutions, agricultural formulations, and electronic chemical and cleaning formulations, including photoresist developer compositions, and these advantages include:
water-borne coatings, inks, adhesives, fountain solutions, agricultural formulations, and electronic chemical formulations which may be applied to a variety of substrates with excellent wetting of substrate surfaces;
a reduction in coating or printing defects such as orange peel and flow/leveling deficiencies;
low surface tension aqueous electronics cleaning and processing solutions, including photoresist developer solutions, which provide good wetting and very low foam;
low-foam surfactants capable of reducing surface tension;
water-borne compositions using a surfactant derived from natural, renewable resources, thus making such formulations environmentally favorable.
Because of their surfactant properties and the ability to control foam, these materials are likely to find applicability in many applications in which the reduction in surface tension and low foam are important. Such applications in which low foam is important include various wet-processing textile operations, such as the dyeing of fibers, fiber scouring, and kier boiling, where low-foaming properties would be particularly advantageous; they may also have applicability in soaps, water-based perfumes, shampoos, detergents, cosmetics and food processing where their marked ability to lower surface tension, and at the same time produce substantially no foam would be highly desirable.
This invention relates to the use of N,Nxe2x80x2-dialkylamide compounds of the structure: 
where R1 and R2 are C4-C10 alkyl groups, and preferably at least one of R1 and R2 is a branched C4 to C10 alkyl group, preferably C5 to C10, and most preferably C5 to C8, for the reduction of equilibrium surface tension in water-based compositions containing an organic compound, particularly coating, ink, fountain solution, adhesive, agricultural, and photoresist developer compositions containing organic compounds such as polymeric resins, detergents, herbicides, fungicides, insecticides or plant growth modifying agents. It is also desirable that an aqueous solution of the malamide demonstrate an equilibrium surface tension of less than 52 dynes/cm at a concentration of 5 wt % or less in water at 25xc2x0 C. using the Wilhelmy plate method.
In one aspect of the invention the malamides of the above formula display excellent ability to reduce equilibrium surface tension while producing little to no foam.
These materials may be prepared by the reaction of primary amines with malic acid or malic acid esters. The reaction is illustrated below: 
The amination reaction may be performed using a variety of conditions as described in the Kirk-Othmer Encyclopedia of Chemical Technology, 4th Ed., Vol. 2, pp. 348-351. The preferred method involves the reaction of a malic acid ester with 2 or more equivalents amine in a protic solvent.
All primary amines or mixtures of primary amines containing at least one C4 to C10 branched alkyl amine may be utilized for the preparation of the N,Nxe2x80x2-dialkylmalamides of this invention, with amines containing 5-10 carbons being preferred and those containing 5-8 carbons being especially preferred. The N,Nxe2x80x2-dialkylmalamides may contain a total of 8-20 amide alkyl carbon atoms, with those containing a total of 10-20 amide alkyl carbons being preferred and those containing a total of 10-16 amide alkyl carbons being especially preferred. Alkyl groups which are suitable should have sufficient carbon to confer surface activity (i.e. an ability to reduce the surface tension of water) to the material but not enough carbon to decrease the solubility to the extent that the ability of the material to reduce surface tension is insufficient for a particular application. Generally, in the practice of this invention, it is desirable to choose amide alkyl groups such that the resulting N,Nxe2x80x2-dialkylmalamides have a solubility that affords the desired surface tension reduction.
The alkyl groups in the malamides of this invention may be the same or different and may be linear or branched, as long as at least one of the alkyl groups is a branched alkyl group. Examples of suitable branched alkyl groups are isobutyl, sec-butyl, 2-pentyl, 3-pentyl, isopentyl, neopentyl, 2-methylbutyl, 3-methyl-2-butyl, 2-hexyl, 3-hexyl, 2-ethylbutyl, 4-methyl-2-pentyl, 2-ethylhexyl, and so on. Of the malamide derivatives those which contain a total of 10 to 20 amide alkyl carbons are preferred and those containing 10 to 16 alkyl carbons most preferred, especially in the cases where R1=R2=isopentyl and where R1=R2=2-ethylhexyl.
An amount of dialkylmalamide compound that is effective to reduce the equilibrium surface tension of the water-based, inorganic or organic compound-containing composition is added. Such effective amount may range from 0.001 to 20 wt %, preferably 0.01 to 10 wt %, and most preferably 0.05 to 5 wt %, of the aqueous composition. Naturally, the most effective amount will depend on the particular application and the solubility of the malamide.
The dialkylmalamides are suitable for use in an aqueous composition comprising in water an inorganic compound which is a mineral ore or a pigment or an organic compound which is a pigment, a polymerizable monomer, such as addition, condensation and vinyl monomers, an oligomeric resin, a polymeric resin, a detergent, a caustic cleaning agent, a herbicide, a fungicide, an insecticide, or a plant growth modifying agent.
In the following water-based organic coating, ink, adhesive, fountain solution, agricultural and photoresist developer compositions containing a dialkyimalamide according to the invention, the other listed components of such compositions are those materials well known to the workers in the relevant art.
A typical water-based protective or decorative organic coating composition to which the dialkylmalamide surfactants of the invention may be added would comprise in an aqueous medium 30 to 80 wt % of a coating composition containing the following components:
A typical water-based ink composition to which the dialkylmalamide surfactants of the invention may be added would comprise in an aqueous medium 20 to 60 wt % of an ink composition containing the following components:
A typical water-based agricultural composition to which the dialkylmalamide surfactants of the invention may be added would comprise in an aqueous medium 0.1 to 80 wt % of an agricultural composition containing the following components:
A typical water-based fountain solution composition for planographic printing would comprise the following components:
A typical water-based adhesive composition to which the dialkylmalamide surfactants of the invention may be added would comprise in an aqueous medium 30 to 65 wt % of an adhesive composition containing the following components:
A typical water-based photoresist developer or electronic cleaning composition to which the N,Nxe2x80x2-dialkylmalamide surfactants of the invention may be added would comprise the following components:
Examples 1-3 illustrate the synthesis of various N,Nxe2x80x2-dialkylmalamides of this invention. All N,Nxe2x80x2-dialkylmalamides were synthesized and then characterized by Nuclear Magnetic Resonance (NMR) spectroscopy. All malamides prepared ranged from 85% to  greater than 99% pure.